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Sequencer System Control Parameters
A sequencer uses a sensor value and compares this value to an operator defined setpoint to control the refrigera-
tion load. This system control parameter may be a suction pressure, a process temperature or any other reading
that provides an accurate indication of the required refrigeration load.
Sequencer Staging Control
The sequencer starts and stops compressors based on operator defined parameters. Independent parameters may
be defined for loading and unloading conditions. The control parameters described below are modified using the
sequencer setpoints and sequencer control group select screens.
Control Setpoint - The control setpoint defines the desired level for the system control parameter. The
sequencer will take action based on the difference between the system control parameter and the setpoint.
The setpoint value is also transmitted to the compressors to be used in automatic capacity control while in
the sequence mode.
Control Deadband - The load and unload deadbands define a zone around the control setpoint where no
staging actions will be taken. If the difference between the setpoint and the system control parameter is less
than the load or unload deadband, no staging will be performed. The deadband values for loading and
unloading are transmitted to the compressors to be used in automatic capacity control while in sequenced
mode.
Normal Bandwidth - The load and unload bandwidths are used to define the difference between normal
staging and fast staging. If the difference between the system control parameter and the setpoint is outside
the deadband but within the bandwidth the normal stage delay is used. If the difference is greater then the
bandwidth the fast stage delay time is used. The normal bandwidth values for loading and unloading are
transmitted to the compressors to be used in automatic capacity control while in sequenced mode.
Normal Stage Delay - The load and unload normal stage delays are used to reduce unnecessary compressor
stops or starts. The sequencer will delay this amount of time before taking action when the difference
between the system control parameter and the setpoint is outside the deadband but within the bandwidth
and the trim machine is fully loaded. Setting the normal stage delay to zero will disable normal stage delay
staging.
Fast Stage Delay - The load and unload fast stage delays are used to allow quick action to be taken when the
system control parameter is far above or below the setpoint. The sequencer will delay this amount of time
before taking action when the system control parameter is outside the bandwidth.
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